1. Field of the Invention
The present invention relates to electric circuits, and more particularly to a semiconductor circuit, an AD converter, an electronic device, or a receiver with an amplifier, a current supply circuit for supplying a current to the amplifier, and a method for controlling a current to be supplied to the amplifier.
2. Description of the Related Art
An example of the circuits for converting an input analog signal to a digital signal is a pipelined AD converter. The pipelined AD converter includes low-bit sub-AD converters which are arranged in multiple stages to allow each of the sub-AD converters to perform AD conversion in a stepwise manner. The pipelined AD converter is configured such that an operational amplifier is interposed between the stages of the sub-AD converters to amplify an input analog signal to the sub-AD converter in the next stage.
A single pipelined AD converter may be operated at a plurality of different operational frequencies in a device incorporating the pipelined AD converter. In this case, it is necessary to design the circuit to the most demanding characteristics among those operation modes, i.e., to the operation at the highest frequency. In general, the higher the operational frequency of the pipelined AD converter, the greater the current consumption required in the operational amplifiers that constitute the converter. Thus, the circuit was designed such that an enough current to operate at the highest frequency among a plurality of operation modes was supplied to the operational amplifiers in all the operation modes.
However, when operated in an operation mode at a lower operational frequency, the circuit designed as described above supplied current more than necessary, causing unnecessary power consumption.
Patent reference 1: Japanese Patent Laid-Open Publication No. 2001-28519